"How do you do?" asked an elderly lady. "I am wonderful and I can see you are too," beamed back David Norris. "Mr Norris, welcome to Galway sir," said a courtly gentleman. A group of 14-year-old girls waited to have their photo taken with the 67-year-old independent senator as a busker dedicated a song to Norris. A doughnut seller gave him a free doughnut. Everyone – young, old, men, women, gay, straight – wanted to shake hands with Norris and wish him luck.

Watching Norris stroll the streets of Galway 10 days ago was to witness an extraordinary political phenomenon in the modern era: a vote-seeking politician whom people did not treat with disdain or indifference.

Judging by the verdict of the streets, Norris was a nailed-on certainty to become Ireland's new president in the October elections. He would have been the first openly gay president anywhere in the world.

But this witty, boastful, posh, Protestant, piano-playing, unashamedly intellectual Joycean scholar has now abruptly quit Ireland's presidential race, sunk by the latest in a series of damaging revelations related to his sexuality – and judgment.

While ordinary people in supposedly socially conservative Ireland seemed sanguine about the idea of a clever and openly gay man becoming their president, there were clearly critics determined to root out every misjudgment in his long and highly respected career as a senator campaigning for gay rights.

Two months ago, a nine-year-old interview was dug up in which Norris unwisely discussed an ancient Greek tradition of older men taking responsibility for the intellectual and sexual education of younger men. This intellectual foray forced him to repeatedly deny that he condoned paedophilia. Norris was damaged but fought on, his lead in the polls apparently undiminished.

Last weekend, however, his campaign was thrown into terminal disarray when a blogger revealed that 14 years ago Norris wrote a letter to an Israeli court appealing for mercy over the conviction of his former lover, Ezra Yizhak, for having sex with a 15-year-old boy. Senior figures in his campaign team quit alongside ordinary volunteers, who had been recruited on a wave of online enthusiasm that was compared to Barack Obama's campaign.

Spending a day with Norris in Galway was to watch a politician with a genius for making connections. The senator was 130 miles from his Dublin home (filled with 10,000 books) but he could have been in his local village. If he did not know everyone, he had something smart to say about their family name or place of birth. And he was never lost for words.

There were many improbabilities about his popularity in Ireland. Norris had been fiercely critical of the pope, was a member of the Church of Ireland rather than the Catholic church, and his father was English. He was a radical liberal who questioned Ireland's love affair with alcohol and was in favour of legalising drugs. Although there was something of Boris Johnson in his smart loquaciousness, he would be far too intellectual for British tastes.

But since Ireland astonished itself in 1990 by electing the feminist human rights lawyer Mary Robinson, it has stuck to a radical template for its presidents. Robinson's successor, Mary McAleese, who stands down this year after serving the maximum two terms, was the first Northern Irish woman to be elected as president. Mired in an economic slump, the mutinous electorate seemed in the mood to turn away from its established parties – as an independent, Norris should have benefited.

Norris had an interesting, radical story to tell. "I don't want to be elected as a gay president. I'm not going to be a gay president. I'm going to be a president who happens to be gay," he told the Guardian in Galway.

As president, Norris said, he would encourage "radical" critical thinking about the global economy. He blamed Ireland's economic meltdown on "the fact that the system was placed above the people. The preservation of the system is more significant to the governments all over Europe – and it's not just Ireland – than the welfare of the people." And he pointed out: "We are in the middle in the biggest transfer of wealth from the poor to the rich that has ever occurred and it's shameful."

Despite the adoration on the streets, however, much media coverage in Ireland was astonishingly vitriolic. "Arrogant, a blabbermouth and ill-suited to being president" was one of the more polite opinion pieces. Critics dared not be directly homophobic but instead argued that Norris was brought down by his own lack of judgment and was too unreliable or reckless to become president.

At one point during the day in Galway, Norris turned and asked whether his campaigning style was different to that in the UK. "I must be less boring than UK politicians," he exclaimed.

Norris will never be boring. Sadly – in the eyes of his many admirers – he will never now be president either.